The invention relates to a method to manufacture an electrically driven air pump, in particular a method to manufacture a secondary air pump for a motor vehicle with an internal combustion engine, or such an electrically driven air pump.
Generic air pumps or fans are used for example as secondary air pumps or secondary ventilation fans to inject additional air into the exhaust gas channel of an internal combustion engine of a motor vehicle. This method minimizes the generation of nitrogen oxides or leads to a reduction in the content of carbon monoxides or hydrocarbons in the combustion residues before the exhaust gas reaches the catalyzer of the internal combustion engine. In the case of a secondary air supply, the exhaust gas channel is supplied with fresh air as immediately as possible behind the engine in order to eliminate the hydrocarbon compounds that are generated during the combustion process and the carbon monoxide. Because of the secondary air supply in the exhaust gas branch, an afterburning of the exhaust gas is practically set into motion, during the course of which the unburned carbon monoxides or hydrocarbons in the engine are afterburned, i.e., subsequently oxidized. In addition, the afterburning via a secondary air supply system increases the exhaust gas temperature so that the operating temperature required for a regulated catalyzer is reached prematurely. Higher temperatures in the exhaust gas branch permit the regulated catalyzer to thereby respond more quickly so that it is able to fulfill its task of eliminating harmful substances sooner during the driving cycle.
Due to the high nominal speed of secondary ventilation fans, which are typically in the range of 20,000 rpm, extremely high requirements for synchronism and thus for the quality of the counterbalancing process are placed on the fan and particularly on the electric motor driving the fan. The vibrations in the air pump that are generated due to imbalances are transmitted to the components that are connected to the air pump and thereby generate increased running noise. It can possibly be necessary to isolate the entire air pump mechanically vis-à-vis other components in order to avoid transmitting vibrations to the vehicle and especially to the passenger compartment.
In order to improve the smoothness of running of such an air pump, removing or applying material to a fan wheel of the pump mechanism is generally known as a means to balance the air pump for example.
An electrically driven air pump is known from EP 0 711 924 B1, which features a housing in which a pump mechanism is arranged on the one side and an electric motor is arranged on the other side. Covers close both the pump-side and motor-side of the housing of the air pump in EP 0 711 924 B1. The electric motor driving the pump mechanism is isolated to a large extent within the pump by means of two elastomer rings, which are supported between the electric motor and the pump housing. The electric motor in this prior art electrically driven air pump is counterbalanced with an installed pump wheel, in a built-in state, with a not yet closed pump side by placing balancing marks on a running wheel of the pump mechanism. Due to the fact that the electric motor is balanced in a built-in state with an installed pump wheel, cooperation of the electric motor with additional components of the air pump can be taken into consideration. Because of the balancing process on the installed electric motor, even though the running quality of such an air pump can be increased by the reduction in the vibrations occurring, manufacturing tolerances cannot be avoided from air pump to air pump, however.